Etiology and Pharmacology of Neuropathic Pain

Microalgae and exercise: from molecular mechanisms and brain health to clinical perspectives in the context of 3P medicine

Microalgae are emerging as innovative bioresources with diverse therapeutic applications, particularly in cardiovascular health, neuroprotection, anti-inflammatory, and antioxidant responses. These bioactive compounds effectively reduce inflammatory mediators, mitigate oxidative stress, and support mitochondrial health-critical factors in exercise performance, recovery, and chronic disease management. Notably, microalgae such as Spirulina and Chlorella exhibit promising biological activities in preclinical and limited clinical studies, including anti-inflammatory and neuroprotective effects. However, large-scale, randomized controlled trials (RCTs) remain scarce, limiting their clinical translation. Although preliminary evidence suggests potential benefits for sports performance, oxidative stress reduction, and cognitive function, most studies are small-scale, preclinical, or observational. Large, well-powered RCTs are needed to confirm their efficacy and safety. Within the framework of Predictive, Preventive, and Personalized Medicine (PPPM/3PM), this review explores microalgae's potential in predictive diagnostics, targeted prevention, and individualized supplementation strategies. Despite promising findings, clinical application requires a cautious approach due to insufficient high-quality trials supporting microalgae-based interventions in medical practice. Future research should prioritize RCTs, pharmacokinetic studies, and long-term safety assessments to establish evidence-based guidelines for their use in health and disease management.

An overview of the non-procedural treatment options for peripheral neuropathic pain

Peripheral neuropathic pain is common in patients with peripheral nerve injury and can significantly impact both their function and quality of life. There is a wide variety of non-interventional treatment approaches, including pharmacologic therapy, physical/occupational therapy, modalities (therapeutic, mechanical, thermal, etc.), psychology, and lifestyle modification. First line pharmacologic therapy for peripheral neuropathic pain includes gabapentinoids, tricyclic antidepressants, and serotonin-norepinephrine reuptake inhibitors. Other classes of medications, such as topical treatments, opioids, and cannabinoids, have more limited usefulness in treatment but remain part of a treatment regimen. Physical and occupational therapy, psychological interventions, and lifestyle medicine are important adjuncts in the treatment and prevention of future peripheral neuropathic pain. The strength of the evidence supporting each intervention varies, with that for pharmacologic intervention being the strongest. A combination of these options tailored to the individual needs of the patient likely will result in the best treatment outcome for peripheral neuropathic pain.

The postoperative relief of vertigo and migraine in Meniere's disease patients with and without migraine

BACKGROUND

The correlation of Meniere's disease (MD) and migraine remains unclear.

OBJECTIVES

To explore the relation of MD and migraine by analyzing the postoperative relief of vertigo and migraine in MD patients with migraine.

MATERIAL AND METHODS

104 MD patients were enrolled. The monthly vertigo episodes (MVE) and migraine headache index (MHI) were used for assessing effectiveness at pre- and post-endolymphatic sac decompression (ELSD). First, patients were divided into MD with migraine and MD two groups with vertigo relief rates compared. Then, the postoperative relief of vertigo and migraine in MD patients with migraine was analyzed.

RESULTS

The postoperative vertigo relief rates for MD and MD with migraine groups were 46.7% and 40.68% with no significant difference. In MD patients with migraine, postoperative MVE and MHI decreased significantly. The Kappa value calculated for vertigo and migraine outcomes was 0.505. The absence of hypertension was independently predictive of relief of vertigo and migraine. The male was independently predictive for relief of migraine.

CONCLUSIONS AND SIGNIFICANCE

ELSD is effective for MD patients with migraine. The postoperative relief of vertigo and migraine has a certain consistency, suggesting MD and migraine may share some common pathogenesis which may be related to inflammation.

Inhibition of Macrophage Activation by Minocycline Attenuates CCI-Induced Neuropathic Pain

Neuropathic pain is characterized by a high prevalence and associated with a variety of disorders of the peripheral and central nervous systems. It remains a major challenge for clinical management due to lack effective treatments. Our previous studies have demonstrated that nerve injury-induced neuroinflammation plays a critical role in regulating the development and maintenance of neuropathic pain. In the present study, we found that chronic constriction injury (CCI) led to a significant increase in the number of macrophages at the site of injured nerves. To elucidate the role of macrophage activation in CCI-induced neuropathic pain, we employed chemical agents, including clodronate liposomes, which is known for their ability to deplete macrophages, and minocycline, an inhibitor of macrophage function. Both intravenous injection of liposome-encapsulated clodronate and intrasciatic delivery of minocycline effectively attenuated CCI-induced mechanical and heat hyperalgesia. Furthermore, transfer of polarized M2 macrophages significantly alleviated CCI-induced neuropathic pain, but not under the condition of M1 macrophage transfer. Mechanistically, our findings indicated that pretreatment with minocycline increased the expression level of CD206 but decreased that of IL-1β, while post-polarization treatment markedly decreased the expression level of both. Additionally, an in vitro migration assay revealed that minocycline exerts an inhibitory effect on macrophage migration. In brief, our study elucidates the effect of CCI-induced macrophage activation on neuropathic pain and provides new insights into the potential clinical application of minocycline for managing neuropathic pain.

The Role of Cytokines in Postherpetic Neuralgia

Nerve injury is a significant cause of postherpetic neuralgia (PHN). It is marked by upregulated expression of cytokines secreted by immune cells such as tumor necrosis factor alpha, interleukin 1 beta (IL-1β), IL-6, IL-18, and IL-10. In neuropathic pain (NP) due to nerve injury, cytokines are important for the induction of neuroinflammation, activation of glial cells, and expression of cation channels. The release of chemokines due to nerve injury promotes immune cell infiltration, recruiting inflammatory cytokines and further amplifying the inflammatory response. The resulting disequilibrium in neuroimmune response and neuroinflammation leads to a reduction of nerve fibers, altered nerve excitability, and neuralgia. PHN is a typical NP and cytokines may induce PHN by promoting central and peripheral sensitization. Currently, treating PHN is challenging and research on the role of cytokine signaling pathways in PHN is lacking. This review summarizes the potential mechanisms of cytokine-mediated PHN and discusses the cytokine signaling pathways associated with the central and peripheral sensitization of PHN. By elucidating the mechanisms of cytokines, the cells and molecules that regulate cytokines, and their signaling systems in PHN, this review reveals important research developments regarding cytokines and their signaling pathways mediating PHN, highlighting new targets of action for the development of analgesic drugs.

Electroacupuncture at 5/100 Hz alleviates neuropathic pain in rats by inhibiting the CCL3/CCR5 axis in the spinal cord

OBJECTIVE

Typically, neuropathic pain (NP) is difficult to manage as it is refractory to conventional medications. Electroacupuncture (EA) at 5/100 Hz has emerged as an effective and promising treatment for NP; however, its mechanism of action is still uncertain. Accordingly, this study investigated the alleviatory mechanism of EA in chronic compression injury (CCI)-induced chronic pain via the C-C chemokine ligand 3 / C-C chemokine receptor type 5 (CCL3/CCR5) axis.

METHODS

The CCI model was established in rats to induce NP. Mechanical and thermal hyperalgesia were assessed with von Frey and Hargreaves tests, respectively. From day 8 after CCI, EA (5/100 Hz) was performed for 1 week (30 min/day). CCL3 and CCR5 expression was detected with Western blotting and immunofluorescence. Glial cell activation was determined through co-labeling of neurons and glial cells with antibodies against CCL3 and CCR5. The release of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α was tested with enzyme-linked immunosorbent assay (ELISA).

RESULTS

EA markedly ameliorated CCI-induced chronic NP in rats and reduced CCL3 and CCR5 expression in the rat spinal cord. CCL3 and CCR5 were co-expressed by neurons and microglia in the central nervous system. In addition, EA also repressed the activation of glial cells and levels of IL-1β, IL-6 and TNF-α.

CONCLUSION

EA may mitigate chronic NP in rats by blocking the CCL3/CCR5 axis in the spinal cord. In addition, EA appeared to exert anti-inflammatory and analgesic effects by suppressing glial cell activation. These findings add to our understanding of the mechanism of EA-induced analgesia.

Mechanisms and Therapeutic Prospects of Microglia-Astrocyte Interactions in Neuropathic Pain Following Spinal Cord Injury

Neuropathic pain is a prevalent and debilitating condition experienced by the majority of individuals with spinal cord injury (SCI). The complex pathophysiology of neuropathic pain, involving continuous activation of microglia and astrocytes, reactive gliosis, and altered neuronal plasticity, poses significant challenges for effective treatment. This review focuses on the pivotal roles of microglia and astrocytes, the two major glial cell types in the central nervous system, in the development and maintenance of neuropathic pain after SCI. We highlight the extensive bidirectional interactions between these cells, mediated by the release of inflammatory mediators, neurotransmitters, and neurotrophic factors, which contribute to the amplification of pain signaling. Understanding the microglia-astrocyte crosstalk and its impact on neuronal function is crucial for developing novel therapeutic strategies targeting neuropathic pain. In addition, this review discusses the fundamental biology, post-injury pain roles, and therapeutic prospects of microglia and astrocytes in neuropathic pain after SCI and elucidates the specific signaling pathways involved. We also speculated that the extracellular matrix (ECM) can affect the glial cells as well. Furthermore, we also mentioned potential targeted therapies, challenges, and progress in clinical trials, as well as new biomarkers and therapeutic targets. Finally, other relevant cell interactions in neuropathic pain and the role of glial cells in other neuropathic pain conditions have been discussed. This review serves as a comprehensive resource for further investigations into the microglia-astrocyte interaction and the detailed mechanisms of neuropathic pain after SCI, with the aim of improving therapeutic efficacy.

Molecule-rich solutions for achieving novel non-opioid analgesics

Despite their efficacy, opioids have long been associated with risks of addiction, tolerance, and dependence, leaving an unmet clinical need for pain treatment. Efforts have been devoted to developing novel classes of pain-relieving medication that outperform current options in terms of pain relief, side-effect profiles, and potential for abuse, but with limited success. Recent advances in the neurobiology of pain have shed light on the potential of targeting non-opioid receptors involved in pain processing. In this review, we identify avenues, ranging from molecular-based approaches to molecule-rich solutions, for effectively identifying non-opioid analgesics free from the side effects associated with opioids.

Kratom Alkaloids, Cannabinoids, and Chronic Pain: Basis of Potential Utility and Role in Therapy

Introduction: Chronic neuropathic pain is as a severe detriment to overall quality of life for millions of Americans. Current pharmacological treatment options for chronic neuropathic pain are generally limited in efficacy and may pose serious adverse effects such as risk of abuse, nausea, dizziness, and cardiovascular events. Therefore, many individuals have resorted to methods of pharmacological self-treatment. This narrative review summarizes the existing literature on the utilization of two novel approaches for the treatment of chronic pain, cannabinoid constituents of Cannabis sativa and alkaloid constituents of Mitragyna speciosa (kratom), and speculates on the potential therapeutic benefits of co-administration of these two classes of compounds. Methods: We conducted a narrative review summarizing the primary motivations for use of both kratom and cannabis products based on epidemiological data and summarize the pre-clinical evidence supporting the application of both kratom alkaloids and cannabinoids for the treatment of chronic pain. Data collection was performed using the PubMed electronic database. The following word combinations were used: kratom and cannabis, kratom and pain, cannabis and pain, kratom and chronic pain, and cannabis and chronic pain. Results: Epidemiological evidence reports that the self-treatment of pain is a primary motivator for use of both kratom and cannabinoid products among adult Americans. Further evidence shows that use of cannabinoid products may precede kratom use, and that a subset of individuals concurrently uses both kratom and cannabinoid products. Despite its growing popularity as a form of self-treatment of pain, there remains an immense gap in knowledge of the therapeutic efficacy of kratom alkaloids for chronic pain in comparison to that of cannabis-based products, with only three pre-clinical studies having been conducted to date. Conclusion: There is sufficient epidemiological evidence to suggest that both kratom and cannabis products are used to self-treat pain, and that some individuals actively use both drugs, which may produce potential additive or synergistic therapeutic benefits that have not yet been characterized. Given the lack of pre-clinical investigation into the potential therapeutic benefits of kratom alkaloids against forms of chronic pain, further research is warranted to better understand its application as a treatment alternative.

Using Integrated Network Pharmacology and Metabolomics to Reveal the Mechanisms of the Combined Intervention of Ligustrazine and Sinomenine in CCI-Induced Neuropathic Pain Rats

Neuropathic pain (NP) is a type of chronic pain resulting from injury or dysfunction of the nerves or spinal cord. Previous studies have shown that the combination of ligustrazine (LGZ) and sinomenine (SIN) exerts a synergistic antinociceptive effect in peripheral and central NP models. On this basis, a comprehensive analgesic evaluation was performed in a chronic constriction injury (CCI)-induced NP model in rats. Sciatic nerve histopathological changes were observed, and 22 cytokines and chemokines levels were analyzed. We also combined network pharmacology and metabolomics to explore their molecular mechanisms. Results showed that the combination of LGZ and SIN significantly alleviated the pain-like behaviors in CCI rats in a time- and dose-dependent manner, demonstrating superior therapeutic effects compared to LGZ or SIN alone. It also improved pathological damage to sciatic nerves and regulated inflammatory cytokine levels. Network pharmacology identified shared and distinct pain-related targets for LGZ and SIN, while metabolomics revealed 54 differential metabolites in plasma, and 17 differential metabolites in CSF were associated with the combined intervention of LGZ and SIN. Finally, through an integrated analysis of the core targets and differential metabolites, tyrosine metabolism, phenylalanine metabolism, and arginine and proline metabolism were identified as potential key metabolic pathways underlying the therapeutic effects of LGZ and SIN in CCI treatment. In conclusion, our study provides evidence to support the clinical application of LGZ and SIN in the treatment of NP.

Identifying neural circuitry abnormalities in neuropathic pain with transcranial magnetic stimulation and electroencephalogram co-registration

Non-invasive brain stimulation (NIBS) technology such as transcranial magnetic stimulation (TMS) represents a promising treatment for neuropathic pain. However, neural circuitries underlying analgesia remain to be established, which is largely limiting treatment responses. Using TMS and electroencephalogram co-registration (TMS-EEG), this study quantified the circuitry abnormalities in neuropathic pain and their associations with pain symptoms. A group of 21 neuropathic pain individuals and 21 healthy controls were assessed with TMS-EEG delivering to the primary motor cortex (M1). With source modelling, local current density and current propagation were analysed with significant current density (SCD) and scattering (SCS) respectively. The SCS and SCD data converged on higher activities in neuropathic pain individuals than healthy controls, within the emotional affective (perigenual anterior cingulate cortex, pgACC), sensory nociceptive (primary somatosensory cortex, S1), and the attentional cognitive (anterior insula, aINS; supracallosal anterior cingulate cortex, scACC) structures of pain. Moreover, current propagation to the pgACC was associated with lower pain-related negative emotions, while current propagation to the aINS with higher pain-related negative emotions. Using concurrent TMS-EEG, our data identified abnormal pain circuitries that could be utilised to improve treatment efficacy with brain stimulation technologies.

Identifying Pain Subtypes in Patients With Craniofacial Lesions of Fibrous Dysplasia/McCune-Albright Syndrome

BACKGROUND

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a genetic disorder, marked by bone lesions, often affecting the craniofacial skeleton. Pain is a prevalent yet heterogeneous symptom reported by patients with craniofacial FD. Effective treatments are currently lacking, posing a significant clinical challenge to patient care.

PURPOSE

This preliminary study examined pain profiles in craniofacial FD and aimed to identify subtypes of patients based on pain phenotypes and emotional health.

STUDY DESIGN, SETTING, SAMPLE

A prospective, cross-sectional study involving 15 patients with FD/MAS, conducted at Boston Children's Hospital and Massachusetts General Brigham's Hospitals.

PREDICTOR/EXPOSURE/INDEPENDENT VARIABLE

Headache frequency, craniofacial pain severity, neuropathic pain quality, pain interference, allodynia, photophobia, depression, and anxiety were assessed using clinical questionnaires.

MAIN OUTCOME VARIABLE(S)

The primary outcome variable was the symptom profile derived from standardized clinical questionnaires and analyzed using principal component analysis and K-means clustering.

COVARIATES

Covariates included demographic data, diagnosis, and lesion location(s).

ANALYSES

Principal component analysis and K-means clustering of patient-reported measures of pain and emotional health were performed. Analysis of variance was conducted to determine significant differences among patient subtypes. Statistical significance was set at (P < .05).

RESULTS

The study included 15 subjects with FD/MAS, with a mean age of 36.2 (13.9) years, including 1 male. Clustering analysis identified 3 subtypes of patients with distinct symptom profiles. Cluster 1 (n = 2) averaged 70 (28.3) headache days in a 90-day period, pain level of 7.5 (0.7) on a 0-10 scale, and severe anxiety, depression, allodynia, photophobia, and pain interference. Cluster 2 (n = 7) patients reported an average of 5.4 (7.5) headache days, an average pain level of 2.7 (2.6), mild or no anxiety, depression, allodynia, photophobia, and pain interference. Cluster 3 (n = 6) patients displayed a mixed symptom profile with an average of 47.3 (36.4) headache days and a pain level of 5.25 (1.4). Notably, patients with temporal and skull base lesions were predominantly found in Clusters 1 and 3, which exhibited the most severe symptomatology.

CONCLUSIONS AND RELEVANCE

This study establishes a basis for future longitudinal research aimed at understanding underlying pain mechanisms and evaluating the response to personalized pain management strategies in subtypes of patients with craniofacial FD.

Beneficial Effects of Exercise in Neuropathic Pain: An Overview of the Mechanisms Involved

Neuropathic pain is a prevalent issue that often arises following injuries to the peripheral or central nervous system. Unfortunately, there is currently no definitive and flawless treatment available to alleviate this type of pain. However, exercise has emerged as a promising nonpharmacological and adjunctive approach, demonstrating a significant impact in reducing pain intensity. This is why physical therapy is considered a beneficial approach for diminishing pain and promoting functional recovery following nerve injuries. Regular physical activity exerts its hypoalgesic effects through a diverse array of mechanisms. These include inhibiting oxidative stress, suppressing inflammation, and modulating neurotransmitter levels, among others. It is possible that multiple activated mechanisms may coexist within an individual. However, the priming mechanism does not need to be the same across all subjects. Each person's response to physical activity and pain modulation may vary depending on their unique physiological and genetic factors. In this review, we aimed to provide a concise overview of the mechanisms underlying the beneficial effects of regular exercise on neuropathic pain. We have discussed several key mechanisms that contribute to the improvement of neuropathic pain through exercise. However, it is important to note that this is not an exhaustive analysis, and there may be other mechanisms at play. Our goal was to provide a brief yet informative exploration of the topic.

Anti-Hyperalgesic Effect of Isopulegol Involves GABA and NMDA Receptors in a Paclitaxel-Induced Neuropathic Pain Model

Background: Neuropathic pain can be triggered by chemotherapy drugs such as paclitaxel (PTX). Management of pain is limited by drugs' ineffectiveness and adverse effects. Isopulegol (ISO) is a monoterpene present in the essential oils of several aromatic plants and has promising pharmacological activities. Objectives: to evaluate the antinociceptive activity of ISO in a PTX-induced neuropathic pain model. Methods: the toxicity of ISO was evaluated in healthy and cancerous cells. Behavioral assessments were performed using the von Frey and acetone tests. We investigated the involvement of the GABAergic pathway, NMDA, TNF-α, and the release of GABA and glutamate in the presence of ISO. Results: ISO showed little or no cytotoxicity in U87 and MDA-MB-231 cells. In both acute and subacute treatment, ISO at doses of 25, 50, and 100 mg/kg (* p < 0.05) increased the mechanical nociceptive threshold of neuropathic animals compared to the control group and reduced thermal sensitivity. Its action was reversed by pre-treatment with flumazenil and potentiated by the NMDA antagonist, MK-801. TNF-α and glutamate levels were reduced and GABA release was increased in the tests carried out. Conclusions: ISO shows low toxicity in neuronal cells and its association with PTX generated synergism in its cytotoxic action. The antinociceptive effect of ISO is due to activation of GABA and antagonism of NMDA receptors and involves the stabilization of neuronal plasma membranes leading to an imbalance in the release of neurotransmitters, favoring GABA-mediated inhibition over glutamatergic excitation.

Unraveling the role of SSH1 in chronic neuropathic pain: A focus on LIMK1 and Cofilin Dephosphorylation in the prefrontal cortex

BACKGROUND AND OBJECTIVE

Neuropathic pain, a debilitating condition stemming from nervous system injuries, has profound impacts on quality of life. The medial prefrontal cortex (mPFC) plays a crucial role in the modulation of pain perception and emotional response. This study explores the involvement of Slingshot Homolog 1 (SSH1) protein in neuropathic pain and related emotional and cognitive dysfunctions in a mouse model of spared nerve injury (SNI).

METHODS

SNI was induced in C57BL/6J mice. SSH1's role was investigated via its overexpression and knockdown using lentiviral vectors in the mPFC. Behavioral assays (thermal and mechanical allodynia, open field test, elevated plus maze, tail suspension test, Y-maze, and novel object recognition were conducted to assess pain sensitivity, anxiety, depression, and cognitive function. Tissue samples underwent Hematoxylin and Eosin staining, Western blotting, immunofluorescence, co-immunoprecipitation, and enzyme-linked immunosorbent assay for inflammatory markers.

RESULTS

SNI mice displayed significant reductions in neuronal density and dendritic integrity in the mPFC, alongside heightened pain perception and emotional disturbances, as compared to sham controls. Overexpression of SSH1 ameliorated these alterations, improving mechanical and thermal thresholds, reducing anxiety and depressive behaviors, and enhancing cognitive performance. Conversely, SSH1 knockdown exacerbated these phenotypes. Molecular investigations revealed that SSH1 modulates pain processing and neuronal health in the mPFC partially through the dephosphorylation of Cofilin and LIM domain kinase 1 (LIMK1), as evidenced by changes in their phosphorylation states and interaction patterns.

CONCLUSION

SSH1 plays a pivotal role in the modulation of neuropathic pain and associated neuropsychological disturbances in the mPFC of mice. Manipulating SSH1 expression can potentially reverse the neurophysiological and behavioral abnormalities induced by SNI, highlighting a promising therapeutic target for treating neuropathic pain and its complex comorbidities.

Activation of GPR55 alleviates neuropathic pain and chronic inflammation

Neuropathic pain (NP) significantly impacts the quality of life due to its prolonged duration and lack of effective treatment. Recent findings suggest that targeting neuroinflammation is a promising approach for treating NP. G protein-coupled receptor 55 (GPR55), a member of the GPCR family, plays an important role in neuroinflammatory regulation. CID16020046, a GPR55 agonist, possesses promising anti-neuroinflammatory effects. Herein, the therapeutic effect of CID16020046 on NP was investigated in an NP rat model. The NP model was established using the unilateral sciatic nerve chronic constriction injury (CCI) assay. Both sham and CCI rats were intraperitoneally administered with 20 mg/kg CID16020046. NP was assessed using paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). First, we showed that GPR55 was downregulated in the spinal dorsal horn of CCI rats. After CCI rats were treated with CID16020046, the values of PWT and PWL were increased, indicating their effect on pain relief. The treated rats had attenuated release of inflammatory cytokines in the spinal cord, decreased spinal malondialdehyde (MDA) levels, and increased spinal glutathione peroxidase (GSH-PX) activity. Additionally, the increased levels of phosphorylated nuclear factor (NF)-κB p65 in CCI rats were significantly alleviated by CID16020046 treatment. Mechanistically, we showed that CID16020046 significantly suppressed the activation of the Janus kinase (JAK2)/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway in the spinal cord of CCI-treated rats. However, Colivelin TFA (a STAT3 agonist) abolished the effect of CID16020046 on JAK2/STAT3 activation. In conclusion, our data demonstrate that the activation of GPR55 by CID16020046 alleviates NP and neuroinflammation in CCI rats by mediating the JAK2/STAT3 pathway.

Pathophysiology-Directed Engineering of a Combination Nanoanalgesic for Neuropathic Pain

Neuropathic pain, one of the most refractory pain diseases, remains a formidable medical challenge. There is still an unmet demand for effective and safe therapies to address this condition. Herein, a rat model of nerve injury-induced neuropathic pain is first established to explore its pathophysiological characteristics. Recognizing the role of neuroinflammation, an inflammation-resolving amphiphilic conjugate PPT is designed and synthesized by simultaneously conjugating polyethylene glycol, phenylboronic acid pinacol ester, and Tempol onto a cyclic scaffold. PPT can self-assemble into nanomicelles (termed PPTN). Following intravenous injection, PPTN preferentially accumulates in the injured nerve, ameliorates the neuroinflammatory milieu, and promotes nerve regeneration, thereby shortening neuropathic pain duration in rats. Moreover, the Ca2+ channel α2δ1 subunit is identified as a therapeutic target by RNA-sequencing analysis of the injured nerve. Based on this target, a mimicking peptide (AD peptide) is screened as an analgesic. By packaging AD peptide into PPTN, a combination nano-analgesic APTN is developed. Besides potentiated anti-hyperalgesic effects due to site-specific delivery and on-demand release of AD peptide at target sites, APTN simultaneously inhibits neuroinflammation and promotes nerve regeneration by reprogramming macrophages via regulating MAPK/NF-kB signaling pathways and NLRP3 inflammasome activation, thus affording synergistic efficacies in treating nerve injury-induced neuropathic pain.

Analysis of postmarketing neuropsychiatric adverse events of avapritinib based on the FDA adverse event reporting system

Neuropsychiatric adverse events (AEs) significantly impact the quality of life of patients using avapritinib. However, the majority of current data comes from pre-marketing, with limited real-world studies. Our research aimed to explore post-marketing data of avapritinib. We evaluated the signals of avapritinib-related neuropsychiatric AEs by data mining using the FDA Adverse Event Reporting System (FAERS). Reporting odds ratio (ROR) and information component (IC) were employed to quantify the signals from the first quarter of 2020 through the fourth quarter of 2023. Subsequently, stratified analyses were conducted to further explore the effect of different stratification schemes on the association between avapritinib and neuropsychiatric AEs. Finally, a combination medication analysis was conducted to explore the impact of the co-administration of neuropsychiatric AEs. A total of 2029 neuropsychiatric AEs were reported, and 49 signals were detected, of which 5 were determined to be new signals. Avapritinib was significantly associated with the occurrence of neuropsychiatric AEs (ROR: 1.52, 95% CI: 1.44-1.61; IC: 0.43, IC025: 0.35). The stratified analysis found that gender, age and eight preferred terms (PTs), including cerebral haemorrhage, may affect the severity of AEs. Combination medication analysis showed that combining avapritinib with 19 other medications, including prochlorperazine, may increase the risk of neuropsychiatric AEs. The median time-to-onset (TTO) of avapritinib-related neuropsychiatric AEs was 32 (interquartile range [IQR] 2-200) days, with about 65% of cases occurring within the first three months of treatment. An increase in the signal for neuropsychiatric AEs was identified in post-marketing studies of avapritinib. Clinicians are advised to remain vigilant for such events, particularly during the initial stages of treatment with avapritinib.

Facilitation of Ca V 3.2 channel gating in pain pathways reveals a novel mechanism of serum-induced hyperalgesia

The Ca V 3.2 isoform of T-type voltage-gated calcium channels plays a crucial role in regulating the excitability of nociceptive neurons; the endogenous molecules that modulate its activity, however, remain poorly understood. Here, we used serum proteomics and patch-clamp physiology to discover a novel peptide albumin (1-26) that facilitates channel gating by chelating trace metals that tonically inhibit Ca V 3.2 via H191 residue. Importantly, serum also potently modulated T-currents in human and rodent dorsal root ganglion (DRG) neurons. In vivo pain studies revealed that injections of serum and albumin (1-26) peptide resulted in robust mechanical and heat hypersensitivity. This hypersensitivity was abolished with a T-channel inhibitor, in Ca V 3.2 null mice and in Ca V 3.2 H191Q knock-in mice. The discovery of endogenous chelators of trace metals in the serum deepens our understanding of the role of Ca V 3.2 channels in neuronal hyperexcitability and may facilitate the design of novel analgesics with unique mechanisms of action.

Comparative outcomes of microsurgical dorsal root entry zone lesioning (DREZotomy) for intractable neuropathic pain in spinal cord and cauda equina injuries

Treatment of neuropathic pain in patients with spinal cord injury (SCI) and cauda equina injury (CEI) remains challenging. Dorsal root entry zone lesioning (DREZL) or DREZotomy is a viable surgical option for refractory cases. This study aimed to compare DREZL surgical outcomes between patients with SCI and those with CEI and to identify predictors of postoperative pain relief. We retrospectively analyzed 12 patients (6 with SCI and 6 with CEI) with intractable neuropathic pain who underwent DREZL. The data collected were demographic characteristics, pain distribution, and outcomes assessed by numeric pain rating scores. Variables and percentages of pain improvement at 1 year and long-term were statistically compared between the SCI and CEI groups. The demographic characteristics and percentage of patients who experienced pain improvement at 1 year postoperatively did not differ between the groups. Compared with the SCI group, the CEI group presented significantly better long-term pain reduction (p = 0.020) and favorable operative outcomes (p = 0.015). Patients with border zone pain had significantly better long-term pain relief and outcomes than did those with diffuse pain (p = 0.008 and p = 0.010, respectively). Recurrent pain after DREZL occurred in the SCI group but not in the CEI group. DREZL provided superior pain relief in patients with CEI. The presence of border zone pain predicted favorable outcomes. CEI patients or SCI patients with border zone pain are good surgical candidates for DREZL, whereas SCI patients with below-injury diffuse pain are poor candidates.

Intrathecal Fumagillin Alleviates Chronic Neuropathy-Induced Nociceptive Sensitization and Modulates Spinal Astrocyte-Neuronal Glycolytic and Angiogenic Proteins

Nociceptive sensitization is accompanied by the upregulation of glycolysis in the central nervous system in neuropathic pain. Growing evidence has demonstrated glycolysis and angiogenesis to be related to the inflammatory processes. This study investigated whether fumagillin inhibits neuropathic pain by regulating glycolysis and angiogenesis. Fumagillin was administered through an intrathecal catheter implanted in rats with chronic constriction injury (CCI) of the sciatic nerve. Nociceptive, behavioral, and immunohistochemical analyses were performed to evaluate the effects of the inhibition of spinal glycolysis-related enzymes and angiogenic factors on CCI-induced neuropathic pain. Fumagillin reduced CCI-induced thermal hyperalgesia and mechanical allodynia from postoperative days (POD) 7 to 14. The expression of angiogenic factors, vascular endothelial growth factor (VEGF) and angiopoietin 2 (ANG2), increased in the ipsilateral lumbar spinal cord dorsal horn (SCDH) following CCI. The glycolysis-related enzymes, pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) significantly increased in the ipsilateral lumbar SCDH following CCI on POD 7 and 14 compared to those in the control rats. Double immunofluorescence staining indicated that VEGF and PKM2 were predominantly expressed in the astrocytes, whereas ANG2 and LDHA were predominantly expressed in the neurons. Intrathecal infusion of fumagillin significantly reduced the expression of angiogenic factors and glycolytic enzymes upregulated by CCI. The expression of hypoxia-inducible factor-1α (HIF-1α), a crucial transcription factor that regulates angiogenesis and glycolysis, was also upregulated after CCI and inhibited by fumagillin. We concluded that intrathecal fumagillin may reduce the expression of ANG2 and LDHA in neurons and VEGF and PKM2 in the astrocytes of the SCDH, further attenuating spinal angiogenesis in neuropathy-induced nociceptive sensitization. Hence, fumagillin may play a role in the inhibition of peripheral neuropathy-induced neuropathic pain by modulating glycolysis and angiogenesis.

A functional unbalance of TRPM8 and Kv1 channels underlies orofacial cold allodynia induced by peripheral nerve damage

Cold allodynia is a debilitating symptom of orofacial neuropathic pain resulting from trigeminal nerve damage. The molecular and neural bases of this sensory alteration are still poorly understood. Here, using chronic constriction injury (CCI) of the infraorbital nerve (IoN) (IoN-CCI) in mice, combined with behavioral analysis, Ca2+ imaging and patch-clamp recordings of retrogradely labeled IoN neurons in culture, immunohistochemistry, and adeno-associated viral (AAV) vector-based delivery in vivo, we explored the mechanisms underlying the altered orofacial cold sensitivity resulting from axonal damage in this trigeminal branch. We found that cold allodynia induced by IoN-CCI is linked to an increase in the proportion of cold-sensitive neurons (CSNs) contributing to this branch and a shift in their thermal thresholds to higher temperatures. These changes are correlated to a reduction of the Kv1.1-1.2-dependent brake potassium current IKD in IoN CSNs and a rise in the percentage of trigeminal neurons expressing TRPM8. The analysis of the electrophysiological properties of CSNs contributing to the IoN suggests that painful cold hypersensitivity involves the recruitment of silent nociceptive afferents that become sensitive to mild cold in response to nerve damage. Notably, pharmacological suppression of TRPM8 channels and AAV-based transduction of trigeminal neurons with the Kv1.1 channel in vivo effectively reverted the nociceptive phenotype in injured animals. Altogether, our results unveil a crucial role of TRPM8 and Kv1 channels in orofacial cold allodynia, suggesting that both the specific TRPM8-blocking and the AAV-driven expression of potassium channels underlying IKD in trigeminal neurons can be effective tools to revert this damage-triggered sensory alteration.

Application of olfactory ensheathing cells in peripheral nerve injury and its complication with pathological pain

Direct or indirect injury of peripheral nerve can lead to sensory and motor dysfunction, which can lead to pathological pain and seriously affect the quality of life and psychosomatic health of patients. While the internal repair function of the body after peripheral nerve injury is limited. Nerve regeneration is the key factor hindering the recovery of nerve function. At present, there is no effective treatment. Therefore, more and more attention have been paid to the development of foreground treatment to achieve functional recovery after peripheral nerve injury, including relief of pathological pain. Cell transplantation strategy is a therapeutic method with development potential in recent years, which can exert endogenous alternative repair by transplanting exogenous functional bioactive cells to the site of nerve injury. Olfactory ensheathing cells (OECs) are a special kind of glial cells, which have the characteristics of continuous renewal and survival. The mechanisms of promoting nerve regeneration and functional repair and relieving pathological pain by transplantation of OECs to peripheral nerve injury include secretion of a variety of neurotrophic factors, axonal regeneration and myelination, immune regulation, anti-inflammation, neuroprotection, promotion of vascular growth and improvement of inflammatory microenvironment around nerve injury. Different studies have shown that OECs combined with biomaterials have made some progress in the treatment of peripheral nerve injury and pathological pain. These biomaterials enhance the therapeutic effect of OECs. Therefore, the functional role of OECs in peripheral nerve injury and pathological pain was discussed in this paper.Although OECs are in the primary stage of exploration in the repair of peripheral nerve injury and the application of pain, but OECs transplantation may become a prospective therapeutic strategy for the treatment of peripheral nerve injury and pathological pain.

Progress in treatment of pathological neuropathic pain after spinal cord injury

Pathological neuropathic pain is a common complication following spinal cord injury. Due to its high incidence, prolonged duration, tenacity, and limited therapeutic efficacy, it has garnered increasing attention from both basic researchers and clinicians. The pathogenesis of neuropathic pain after spinal cord injury is multifaceted, involving factors such as structural and functional alterations of the central nervous system, pain signal transduction, and inflammatory effects, posing significant challenges to clinical management. Currently, drugs commonly employed in treating spinal cord injury induced neuropathic pain include analgesics, anticonvulsants, antidepressants, and antiepileptics. However, a subset of patients often experiences suboptimal therapeutic responses or severe adverse reactions. Therefore, emerging treatments are emphasizing a combination of pharmacological and non-pharmacological approaches to enhance neuropathic pain management. We provide a comprehensive review of past literature, which aims to aim both the mechanisms and clinical interventions for pathological neuropathic pain following spinal cord injury, offering novel insights for basic science research and clinical practice in spinal cord injury treatment.

Sinomenine Ameliorated Microglial Activation and Neuropathic Pain After Chronic Constriction Injury Via TGF-β1/ALK5/Smad3 Signalling Pathway

Sinomenine (SIN), a bioactive isoquinoline alkaloid extracted from the roots and stems of Sinomenium acutum, is efficacious against various chronic pain conditions. Inhibition of microglial activation at the spinal level contributes to the analgesic effects of SIN. Microglial activation in the spinal dorsal horn is key to sensitising neuropathic pain. Consequently, this study aimed to investigate whether the antinociceptive effects of SIN in neuropathic pain are induced through microglial inhibition and the underlying mechanisms. In this study, we observed that SIN alleviated chronic constriction injury (CCI)-induced pain hypersensitivity, spinal microglial activation and neuroinflammation. Consistently, SIN evoked the upregulation of transforming growth factor-beta1 (TGF-β1) and phosphorylated Smad3 in the L4-6 ipsilateral spinal dorsal horn of CCI mice. Intrathecal injection of TGF-β1 siRNA and an activin receptor-like receptor (ALK5) inhibitor reversed SIN's antinociceptive and antimicroglial effects on CCI mice. Moreover, targeting Smad3 in vitro with siRNA dampened the inhibitory effect of TGF-β1 on lipopolysaccharide-induced microglial activation. Finally, targeting Smad3 abrogated SIN-induced pain relief and microglial inhibition in CCI mice. These findings indicate that the TGF-β1/ALK5/Smad3 axis plays a key role in the antinociceptive effects of SIN on neuropathic pain, indicating its suppressive ability on microglia.

Rate-Dependent Depression of the Hoffmann Reflex: Practical Applications in Painful Diabetic Neuropathy

Measurement of the rate-dependent depression (RDD) of the Hoffmann (H) reflex, a technique developed over half a century ago, is founded on repeated stimulation of the H-reflex with tracking of sequentially evoked H-wave amplitudes in the resulting electromyogram. RDD offers insight into the integrity of spinal reflex pathways and spinal inhibitory regulation. Initially, RDD was predominantly utilized in the mechanistic exploration and evaluation of movement disorders characterized by spasticity symptoms, as may occur following spinal cord injury. However, there is increasing recognition that sensory input from the periphery is modified at the spinal level before ascending to the higher central nervous system and that some pain states can arise from, or be exaggerated by, disruption of spinal processing via a mechanism termed spinal disinhibition. This, along with the urgent clinical need to identify biological markers of pain generator and/or amplifier sites to facilitate targeted pain therapies, has prompted interest in RDD as a biomarker for the contribution of spinal disinhibition to neuropathic pain states. Current research in animals and humans with diabetes has revealed specific disorders of spinal GABAergic function associated with impaired RDD. Future investigations on RDD aim to further elucidate its underlying pathways and enhance its clinical applications.

CBD's potential impact on Parkinson's disease: An updated overview

Background

Parkinson's disease (PD) is primarily known as a motor disorder; however, its debilitating non-motor symptoms have a significant impact on patients' quality of life. The current standard treatment, l-DOPA, is used to relieve motor symptoms, but prolonged use is often associated with severe side effects. This creates an urgent need for effective alternatives targeting both motor and non-motor symptoms.

Objectives

Over the past decade, Cannabis sativa and its cannabinoids have been widely studied across various health conditions. Among these compounds, cannabidiol (CBD), a non-psychoactive component, is garnering growing interest due to its multi-targeted pleiotropic properties. This work aims to provide a comprehensive overview of CBD's efficacy in PD.

Methods

This review compiles data on both motor and non-motor symptoms of PD, integrating results from preclinical animal studies and available clinical trials.

Results

Preclinical research has demonstrated promising results regarding CBD's potential benefits in PD; however, the total number of clinical trials is limited (with only seven studies to date), making it difficult to draw definitive conclusions on its efficacy.

Conclusions

While preclinical findings suggest that CBD may have therapeutic potential in PD, the limited number of clinical trials highlights the need for further research. This review emphasizes the gaps that need to be addressed in future studies to fully understand CBD's role in treating both motor and non-motor symptoms of PD.

Signaling Pathways Concerning Mitochondrial Dysfunction: Implications in Neurodegeneration and Possible Molecular Targets

Mitochondrion is an important organelle present in our cells responsible for meeting energy requirements. All higher organisms rely on efficient mitochondrial bioenergetic machinery to sustain life. No other respiratory process can produce as much power as generated by mitochondria in the form of ATPs. This review is written in order to get an insight into the magnificent working of mitochondrion and its implications in cellular homeostasis, bioenergetics, redox, calcium signaling, and cell death. However, if this machinery gets faulty, it may lead to several disease states. Mitochondrial dysfunctioning is of growing concern today as it is seen in the pathogenesis of several diseases which includes neurodegenerative disorders, cardiovascular disorders, diabetes mellitus, skeletal muscle defects, liver diseases, and so on. To cover all these aspects is beyond the scope of this article; hence, our study is restricted to neurodegenerative disorders only. Moreover, faulty functioning of this organelle can be one of the causes of early ageing in individuals. This review emphasizes mutations in the mitochondrial DNA, defects in oxidative phosphorylation, generation of ROS, and apoptosis. Researchers have looked into new approaches that might be able to control mitochondrial failure and show a lot of promise as treatments.

Machine Learning Elucidates Electrophysiological Properties Predictive of Multi- and Single-Firing Human and Mouse Dorsal Root Ganglia Neurons

Human and mouse dorsal root ganglia (hDRG and mDRG) neurons are important tools in understanding the molecular and electrophysiological mechanisms that underlie nociception and drive pain behaviors. One of the simplest differences in firing phenotypes is that neurons are single-firing (exhibit only one action potential) or multi-firing (exhibit 2 or more action potentials). To determine if single- and multi-firing hDRG neurons exhibit differences in intrinsic properties, firing phenotypes, and AP waveform properties, and if these properties could be used to predict multi-firing, we measured 22 electrophysiological properties by whole-cell patch-clamp electrophysiology of 94 hDRG neurons from six male and four female donors. We then analyzed the data using several machine learning models to determine if these properties could be used to predict multi-firing. We used 1,000 iterations of Monte Carlo cross-validation to split the data into different train and test sets and tested the logistic regression, k-nearest neighbors, random forest, support vector classifier, and XGBoost machine learning models. All models tested had a >80% accuracy on average, with support vector classifier, and XGBoost performing the best. We found that several properties correlated with multi-firing hDRG neurons and together could be used to predict multi-firing neurons in hDRG including a long decay time, a low rheobase, and long first spike latency. We also found that the hDRG models were able to predict multi-firing with 90% accuracy in mDRG neurons. Understanding these properties could be beneficial in the elucidation of targets on peripheral sensory neurons related to pain.

Serum brain-derived neurotrophic factor level in patients with disc induced lumbosacral radiculopathy: Relation to pain severity and functional disability

BACKGROUND

Pain is the major cause of disability in disc induced lumbosacral radiculopathy (LSR) and is related to neurotrophins mainly brain derived neurotrophic factor (BDNF). However, to our knowledge evaluating serum BDNF in disc induced LSR has not been reported before. This study was done to investigate serum BDNF in LSR patients and its relation to pain severity and functional disability.

METHODS

This case-control study included 40 disc induced LSR patients and 40 age and sex matched healthy subjects. All patients were subjected to neurological examination, electrophysiological evaluation, pain severity assessment using numerical rating scale (NRS) and functional disability assessment using Modified Oswestry Low Back Pain Disability Index (ODI) and Maine-Seattle Back Questionnaire (MSBQ). According to Douleur neuropathique 4 (DN4) questionnaire, patients were divided into those with neuropathic pain and those with non-neuropathic pain. Serum BDNF was measured by enzyme-linked immunosorbent assay in all participants.

RESULTS

Serum BDNF was significantly higher in LSR patients than in healthy controls (U=272.5, P<0.001). Moreover, serum BDNF was significantly higher in those with neuropathic pain compared to those with non-neuropathic pain (U=35, P=0.03). Serum BDNF had a significant positive correlation with NRS score among those with acute pain (rs=0.537, P=0.026), however there was no significant correlation among those with chronic pain. Furthermore, BDNF had no significant correlation with modified ODI and MSBQ.

CONCLUSION

Increased serum BDNF may be associated with neuropathic pain and acute pain severity in disc induced LSR. However, it may not be related to chronic pain severity or functional disability.

High-frequency terahertz stimulation alleviates neuropathic pain by inhibiting the pyramidal neuron activity in the anterior cingulate cortex of mice

Neuropathic pain (NP) is caused by a lesion or disease of the somatosensory system and is characterized by abnormal hypersensitivity to stimuli and nociceptive responses to non-noxious stimuli, affecting approximately 7-10% of the general population. However, current first-line drugs like non-steroidal anti-inflammatory agents and opioids have limitations, including dose-limiting side effects, dependence, and tolerability issues. Therefore, developing new interventions for the management of NP is urgent. In this study, we discovered that the high-frequency terahertz stimulation (HFTS) at approximately 36 THz effectively alleviates NP symptoms in mice with spared nerve injury. Computational simulation suggests that the frequency resonates with the carbonyl group in the filter region of Kv1.2 channels, facilitating the translocation of potassium ions. In vivo and in vitro results demonstrate that HFTS reduces the excitability of pyramidal neurons in the anterior cingulate cortex likely through enhancing the voltage-gated K+ and also the leak K+ conductance. This research presents a novel optical intervention strategy with terahertz waves for the treatment of NP and holds promising applications in other nervous system diseases.

Electroacupuncture Relieves Neuropathic Pain via Adenosine 3 Receptor Activation in the Spinal Cord Dorsal Horn of Mice

Neuropathic pain (NPP) is a devastating and unbearable painful condition. As prevailing treatment strategies have failed to mitigate its complications, there remains a demand for effective therapies. Electroacupuncture (EA) has proved a potent remedial strategy in NPP management in humans and mammals. However, past studies have investigated the underlying mechanism of the analgesic effects of EA on NPP, focusing primarily on adenosine receptors in peripheral tissues. Herein, we elucidate the role of the adenosine (Adora-3) signaling pathway in mediating pain relief through EA in the central nervous system, which is obscure in the literature and needs exploration. Specific pathogen-free (SPF) male adult mice (C57BL/6 J) were utilized to investigate the effect of EA on adenosine metabolism (CD73, ADA) and its receptor activation (Adora-3), as potential mechanisms to mitigate NPP in the central nervous system. NPP was induced via spared nerve injury (SNI). EA treatment was administered seven times post-SNI surgery, and lumber (L4-L6) spinal cord was collected to determine the molecular expression of mRNA and protein levels. In the spinal cord of mice, following EA application, the expression results revealed that EA upregulated (p < 0.05) Adora-3 and CD73 by inhibiting ADA expression. In addition, EA triggered the release of adenosine (ADO), which modulated the nociceptive responses and enhanced neuronal activation. Meanwhile, the interplay between ADO levels and EA-induced antinociception, using an Adora-3 agonist and antagonist, showed that the Adora-3 agonist IB-MECA significantly increased (p < 0.05) nociceptive thresholds and expression levels. In contrast, the antagonist MRS1523 exacerbated neuropathic pain. Furthermore, an upregulated effect of EA on Adora-3 expression was inferred when the Adora-3 antagonist was administered, and the EA treatment increased the fluorescent intensity of Adora-3 in the spinal cord. Taken together, EA effectively modulates NPP by regulating the Adora-3 signaling pathway under induced pain conditions. These findings enhance our understanding of NPP management and offer potential avenues for innovative therapeutic interventions.

Neuropharmacology of Neuropathic Pain: A Systematic Review

Neuropathic pain, a debilitating condition, remains challenging to manage effectively. An insight into neuropharmacological mechanisms is critical for optimizing treatment strategies. This systematic review aims to evaluate the role of neuropharmacological agents based on their efficacy, involved neurotransmitters, and receptors. A manual literature search was undertaken in PubMed including Medline, Cochrane Library, Google Scholar, Plos One, Science Direct, and clinicaltrials.gov from 2013 until 2023. Out of the 13 included studies, seven evaluated the role of gabapentinoids. Two main drugs from this group, gabapentin and pregabalin, function by binding voltage-gated calcium channels, lowering neuronal hyperexcitability and pain signal transmission, thereby relieving neuropathic pain. Four of the pooled studies reported the use of tricyclic antidepressants (TCAs) including amitriptyline and nortriptyline which work by blocking the reuptake of norepinephrine and serotonin, their increased concentration is thought to be central to their analgesic effect. Three articles assessed the use of serotonin-norepinephrine reuptake inhibitors (SNRIs) and reported them as effective as the TCAs in managing neuropathic pain. They work by augmenting serotonin and norepinephrine. Three studies focused on the use of selective serotonin reuptake inhibitors (SSRIs), modulating their effect by increasing serotonin levels; however, they were reported as not a highly effective treatment option for neuropathic pain. One of the studies outlined the use of cannabinoids for neuropathic pain by binding to cannabinoid receptors with only mild adverse effects. It is concluded that gabapentinoids, TCAs, and SNRIs were reported as the most effective therapy for neuropathic pain; however, for trigeminal neuralgia, anticonvulsants like carbamazepine were considered the most effective. Opioids were considered second-line drugs for neuropathic pain as they come with adverse effects and a risk of dependence. Ongoing research is exploring novel drugs like ion channels and agents modulating pain pathways for neuropathic pain management. Our review hopes to inspire further research into patient stratification by their physiology, aiding quicker and more accurate management of neuropathic pain while minimizing inadvertent side effects.

Mirogabalin as a Therapeutic Option for Neuropathic Pain Emerging Post-endodontic Treatment: A Two-Case Report

INTRODUCTION

Occlusal and percussion pain may manifest occasionally following endodontic treatment, influencing retreatment decisions. Two cases of periapical neuropathic pain, classified as post-traumatic trigeminal neuropathic pain according to the International Classification of Orofacial Pain, are presented. Although mirogabalin is effective in managing neuropathic pain, there is a lack of clinical reports on its use for occasional post-traumatic trigeminal neuropathic pain after endodontic treatment. These cases highlight clinical symptoms and successful treatment with mirogabalin for post-traumatic trigeminal neuropathic pain after endodontic treatment, providing clinicians a "take-away" lesson for improving patient condition.

METHODS

The patients, referred by their primary dentist due to postendodontic abnormal pain, found no relief with antibiotics or nonsteroidal anti-inflammatory drugs. Although no findings including swelling or periapical radiolucency were observed around the tooth, they experienced occlusal and percussion pain. Local anesthetic testing showed that the pain originated from the peripheral area around the tooth rather than from central sensitization. Dental radiography and cone-beam computed tomography revealed no abnormal findings. Root canal retreatment was performed by a specialist in endodontic treatment. Although endodontic retreatment drastically decreased visual analog scale pain score, pain persisted. Based on the International Classification of Orofacial Pain criteria, diseases other than post-traumatic trigeminal neuropathic pain were excluded. Mirogabalin (10 mg/d) was prescribed once daily before bedtime.

RESULTS

Visual analog scale scores gradually and drastically decreased 2 weeks after mirogabalin therapy. Several months later, no recurrence of postendodontic pain was observed after tapering off and discontinuing mirogabalin.

CONCLUSIONS

These findings suggest the possibility of a new treatment method for post-traumatic trigeminal neuropathic pain after endodontic treatment.

Study on analgesic effect of Shentong Zhuyu Decoction in neuropathic pain rats by network pharmacology and RNA-Seq

ETHNOPHARMACOLOGICAL RELEVANCE

Shentong Zhuyu Decoction (STZYD) is a traditional prescription for promoting the flow of Qi and Blood which is often used in the treatment of low back and leg pain clinicall with unclear mechanism. Neuropathic pain (NP) is caused by disease or injury affecting the somatosensory system. LncRNAs may play a key role in NP by regulating the expression of pain-related genes through binding mRNAs or miRNAs sponge mechanisms.

AIM OF THE STUDY

To investigate the effect and potential mechanism of STZYD on neuropathic pain.

METHODS

Chronic constriction injury (CCI) rats, a commonly used animal model, were used in this study. The target of STZYD in NP was analyzed by network pharmacology, and the analgesic effect of STZYD in different doses (H-STZYD, M-STZYD, L-STZYD) on CCI rats was evaluated by Mechanical withdrawal thresholds (MWT) and thermal withdrawal latency (TWL). Meanwhile, RNA-seq assay was used to detect the changed mRNAs and lncRNAs in CCI rats after STZYD intervention. GO analysis, KEGG pathway analysis, and IPA analysis were used to find key target genes and pathways, verified by qPCR and Western Blot. The regulatory effect of lncRNAs on target genes was predicted by co-expression analysis and ceRNA network construction.

RESULTS

We found that STZYD can improve hyperalgesia in CCI rats, and H-STZYD has the best analgesic effect. The results of network pharmacological analysis showed that STZYD could play an analgesic role in CCI rats through the MAPK/ERK/c-FOS pathway. By mRNA-seq and lncRNA-seq, we found that STZYD could regulate the expression of Cnr1, Cacng5, Gucy1a3, Kitlg, Npy2r, and Grm8, and inhibited the phosphorylation level of ERK in the spinal cord of CCI rats. A total of 27 lncRNAs were associated with the target genes and 30 lncRNAs, 83 miRNAs and 5 mRNAs participated in the ceRNA network.

CONCLUSION

STZYD has the effect of improving hyperalgesia in CCI rats through the MAPK/ERK/c-FOS pathway, which is related to the regulation of lncRNAs to Cnr1 and other key targets.

A novel role for microtubule affinity-regulating kinases in neuropathic pain

BACKGROUND AND PURPOSE

Neuropathic pain affects millions of patients, but there are currently few viable therapeutic options available. Microtubule affinity-regulating kinases (MARKs) regulate the dynamics of microtubules and participate in synaptic remodelling. It is unclear whether these changes are involved in the central sensitization of neuropathic pain. This study examined the role of MARK1 or MARK2 in regulating neurosynaptic plasticity induced by neuropathic pain.

EXPERIMENTAL APPROACH

A rat spinal nerve ligation (SNL) model was established to induce neuropathic pain. The role of MARKs in nociceptive regulation was assessed by genetically knocking down MARK1 or MARK2 in amygdala and systemic administration of PCC0105003, a novel small molecule MARK inhibitor. Cognitive function, anxiety-like behaviours and motor coordination capability were also examined in SNL rats. Synaptic remodelling-associated signalling changes were detected with electrophysiological recording, Golgi-Cox staining, western blotting and qRT-PCR.

KEY RESULTS

MARK1 and MARK2 expression levels in amygdala and spinal dorsal horn were elevated in SNL rats. MARK1 or MARK2 knockdown in amygdala and PCC0105003 treatment partially attenuated pain-like behaviours along with improving cognitive deficit, anxiogenic-like behaviours and motor coordination in SNL rats. Inhibition of MARKs signalling reversed synaptic plasticity at the functional and structural levels by suppressing NR2B/GluR1 and EB3/Drebrin signalling pathways both in amygdala and spinal dorsal horn.

CONCLUSION AND IMPLICATIONS

These results suggest that MARKs-mediated synaptic remodelling plays a key role in the pathogenesis of neuropathic pain and that pharmacological inhibitors of MARKs such as PCC0105003 could represent a novel therapeutic strategy for the management of neuropathic pain.

Effectiveness of Duloxetine versus Other Therapeutic Modalities in Patients with Diabetic Neuropathic Pain: A Systematic Review and Meta-Analysis

Objectives: Diabetic peripheral neuropathy (DPN) is a chronic complication of diabetes mellitus (DM) with symptoms like intense pain and impaired quality of life. This condition has no treatment; instead, the pain is managed with various antidepressants, including duloxetine. The aim of this study is to analyze the evidence on the efficacy of duloxetine in the management of DPN. Methods: A systematic search in different databases was conducted using the keywords "diabetic neuropathy", "duloxetine therapy", "neuropathic pain", and "Diabetes Mellitus". Finally, eight studies were included in this meta-analysis. Results: All articles comparing duloxetine at different doses vs. a placebo reported significant differences in favor of duloxetine on pain scales like 24 h Average Pain Severity (standardized mean difference [SMD] = -1.06, confidence interval [CI] = -1.09 to -1.03, and p < 0.00001) and BPI Severity (SMD = -0.70, CI = -0.72 to -0.68, and p < 0.00001), among others. A total of 75% of the meta-analyses of studies comparing duloxetine at different doses showed a tendency in favor of the 120 mg/d dose. There were significant differences in favor of duloxetine when compared to routine care on the Euro Quality of Life (SMD = -0.04, CI = -0.04 to -0.03, and p < 0.00001) and SF-36 Survey (SMD = -5.86, CI = -6.28 to -5.44, and p < 0.00001) scales. There were no significant differences on the visual analog scale (VAS) when comparing duloxetine and gabapentin. Conclusions: Duloxetine appears to be effective in the management of DPN in different pain, symptom improvement, and quality of life scales.

Machine learning elucidates electrophysiological properties predictive of multi- and single-firing human and mouse dorsal root ganglia neurons

Human and mouse dorsal root ganglia (hDRG and mDRG) neurons are important tools in understanding the molecular and electrophysiological mechanisms that underlie nociception and drive pain behaviors. One of the simplest differences in firing phenotypes is that neurons are single-firing (exhibit only one action potential) or multi-firing (exhibit 2 or more action potentials). To determine if single- and multi-firing hDRG exhibit differences in intrinsic properties, firing phenotypes, and AP waveform properties, and if these properties could be used to predict multi-firing, we measured 22 electrophysiological properties by whole-cell patch-clamp electrophysiology of 94 hDRG neurons from 6 male and 4 female donors. We then analyzed the data using several machine learning models to determine if these properties could be used to predict multi-firing. We used 1000 iterations of Monte Carlo Cross Validation to split the data into different train and test sets and tested the Logistic Regression, k-Nearest Neighbors, Random Forest, Supported Vector Classification, and XGBoost machine learning models. All models tested had a greater than 80% accuracy on average, with Supported Vector Classification and XGBoost performing the best. We found that several properties correlated with multi-firing hDRG neurons and together could be used to predict multi-firing neurons in hDRG including a long decay time, a low rheobase, and long first spike latency. We also found that the hDRG models were able to predict multi-firing with 90% accuracy in mDRG. Targeting the neuronal properties that lead to multi-firing could elucidate better targets for treatment of chronic pain.

BDNF in Neuropathic Pain; the Culprit that Cannot be Apprehended

In males but not in females, brain derived neurotrophic factor (BDNF) plays an obligatory role in the onset and maintenance of neuropathic pain. Afferent terminals of injured peripheral nerves release colony stimulating factor (CSF-1) and other mediators into the dorsal horn. These transform the phenotype of dorsal horn microglia such that they express P2X4 purinoceptors. Activation of these receptors by neuron-derived ATP promotes BDNF release. This microglial-derived BDNF increases synaptic activation of excitatory dorsal horn neurons and decreases that of inhibitory neurons. It also alters the neuronal chloride gradient such the normal inhibitory effect of GABA is converted to excitation. By as yet undefined processes, this attenuated inhibition increases NMDA receptor function. BDNF also promotes the release of pro-inflammatory cytokines from astrocytes. All of these actions culminate in the increase dorsal horn excitability that underlies many forms of neuropathic pain. Peripheral nerve injury also alters excitability of structures in the thalamus, cortex and mesolimbic system that are responsible for pain perception and for the generation of co-morbidities such as anxiety and depression. The weight of evidence from male rodents suggests that this preferential modulation of excitably of supra-spinal pain processing structures also involves the action of microglial-derived BDNF. Possible mechanisms promoting the preferential release of BDNF in pain signaling structures are discussed. In females, invading T-lymphocytes increase dorsal horn excitability but it remains to be determined whether similar processes operate in supra-spinal structures. Despite its ubiquitous role in pain aetiology neither BDNF nor TrkB receptors represent potential therapeutic targets.

In vitro models for neuropathic pain phenotypic screening in brain therapeutics

The discovery of brain therapeutics faces a significant challenge due to the low translatability of preclinical results into clinical success. To address this gap, several efforts have been made to obtain more translatable neuronal models for phenotypic screening. These models allow the selection of active compounds without predetermined knowledge of drug targets. In this review, we present an overview of various existing models within the field, examining their strengths and limitations, particularly in the context of neuropathic pain research. We illustrate the usefulness of these models through a comparative review in three crucial areas: i) the development of novel phenotypic screening strategies specifically for neuropathic pain, ii) the validation of the models for both primary and secondary screening assays, and iii) the use of the models in target deconvolution processes.

Electroacupuncture suppresses neuronal ferroptosis to relieve chronic neuropathic pain

Growing evidence supports the analgesic efficacy of electroacupuncture (EA) in managing chronic neuropathic pain (NP) in both patients and NP models induced by peripheral nerve injury. However, the underlying mechanisms remain incompletely understood. Ferroptosis, a novel form of programmed cell death, has been found to be activated during NP development, while EA has shown potential in promoting neurological recovery following acute cerebral injury by targeting ferroptosis. In this study, to investigate the detailed mechanism underlying EA intervention on NP, male Sprague-Dawley rats with chronic constriction injury (CCI)-induced NP model received EA treatment at acupoints ST36 and GV20 for 14 days. Results demonstrated that EA effectively attenuated CCI-induced pain hypersensitivity and mitigated neuron damage and loss in the spinal cord of NP rats. Moreover, EA reversed the oxidative stress-mediated spinal ferroptosis phenotype by upregulating reduced expression of xCT, glutathione peroxidase 4 (GPX4), ferritin heavy chain (FTH1) and superoxide dismutase (SOD) levels, and downregulating increased expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), malondialdehyde levels and iron overload. Furthermore, EA increased the immunofluorescence co-staining of GPX4 in neurons cells of the spinal cord of CCI rats. Mechanistic analysis unveiled that the inhibition of antioxidant pathway of Nrf2 signalling via its specific inhibitor, ML385, significantly countered EA's protective effect against neuronal ferroptosis in NP rats while marginally diminishing its analgesic effect. These findings suggest that EA treatment at acupoints ST36 and GV20 may protect against NP by inhibiting neuronal ferroptosis in the spinal cord, partially through the activation of Nrf2 signalling.

Cellular and molecular mechanisms involved in the analgesic effects of botulinum neurotoxin: A literature review

Botulinum neurotoxins (BoNTs), derived from Clostridium botulinum, have been employed to treat a range of central and peripheral neurological disease. Some studies indicate that BoNT may be beneficial for pain conditions as well. It has been hypothesized that BoNTs may exert their analgesic effects by preventing the release of pain-related neurotransmitters and neuroinflammatory agents from sensory nerve endings, suppressing glial activation, and inhibiting the transmission of pain-related receptors to the neuronal cell membrane. In addition, there is evidence to suggest that the central analgesic effects of BoNTs are mediated through their retrograde axonal transport. The purpose of this review is to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions. Most of the studies reviewed in this article were conducted using BoNT/A. The PubMed database was searched from 1995 to December 2022 to identify relevant literature.

The Unpredictable Ulnar Nerve-Ulnar Nerve Entrapment from Anatomical, Pathophysiological, and Biopsychosocial Aspects

Peripheral nerves consist of delicate structures, including a rich microvascular system, that protect and nourish axons and associated Schwann cells. Nerves are sensitive to internal and external trauma, such as compression and stretching. Ulnar nerve entrapment, the second most prevalent nerve entrapment disorder after carpal tunnel syndrome, appears frequently at the elbow. Although often idiopathic, known risk factors, including obesity, smoking, diabetes, and vibration exposure, occur. It exists in all adult ages (mean age 40-50 years), but seldom affects individuals in their adolescence or younger. The patient population is heterogeneous with great co-morbidity, including other nerve entrapment disorders. Typical early symptoms are paresthesia and numbness in the ulnar fingers, followed by decreased sensory function and muscle weakness. Pre- and postoperative neuropathic pain is relatively common, independent of other symptom severity, with a risk for serious consequences. A multimodal treatment strategy is necessary. Mild to moderate symptoms are usually treated conservatively, while surgery is an option when conservative treatment fails or in severe cases. The decision to perform surgery might be difficult, and the outcome is unpredictable with the risk of complications. There is no consensus on the choice of surgical method, but simple decompression is relatively effective with a lower complication rate than transposition.

Spinal interleukin-24 contributes to neuropathic pain after peripheral nerve injury through interleukin-20 receptor2 in mice

Neuroinflammation is critically involved in nerve injury-induced neuropathic pain, characterized by local and systemic increased levels of proinflammatory cytokines. Interleukin-24 (IL-24), a key member of the IL-10 family, has been extensively studied for its therapeutic potential in various diseases, including cancer, autoimmune disorders, and bacterial infections, but whether it is involved in the regulation of neuropathic pain caused by peripheral nerve injury (PNI) has not been well established. In this study, we reported that spared nerve injury (SNI) induced a significant upregulation of IL-24 in fibroblasts, neurons, and oligodendrocyte precursor cells (OPCs, also called NG2-glia) in the affected spinal dorsal horns (SDHs), as well as dorsal root ganglions (DRGs). We also found that tumor necrosis factor α (TNF-α) induced the transcriptional expression of IL-24 in cultured fibroblasts, neurons, and NG2-glia; in addition, astrocytes, microglia, and NG2-glia treated with TNF-α exhibited a prominent increase in interleukin-20 receptor 2 (IL-20R2) expression. Furthermore, we evaluated the ability of IL-24 and IL-20R2 to attenuate pain in preclinical models of neuropathic pain. Intrathecal (i.t.) injection of IL-24 neutralizing antibody or IL-20R2 neutralizing antibody could effectively alleviate mechanical allodynia and thermal hyperalgesia after PNI. Similarly, intrathecal injection of IL-24 siRNA or IL-20R2 siRNA also alleviated mechanical allodynia after SNI. The inhibition of IL-24 reduced SNI-induced proinflammatory cytokine (IL-1β and TNF-α) production and increased anti-inflammatory cytokine (IL-10) production. Meanwhile, the inhibition of IL-20R2 also decreased IL-1β mRNA expression after SNI. Collectively, our findings revealed that IL-24/IL-20R might contribute to neuropathic pain through inflammatory response. Therefore, targeting IL-24 could be a promising strategy for treating neuropathic pain induced by PNI.

Mechanism of Analgesia by Gabapentinoid Drugs: Involvement of Modulation of Synaptogenesis and Trafficking of Glutamate-Gated Ion Channels

Gabapentinoids have clinically been used for treating epilepsy, neuropathic pain, and several other neurologic disorders for >30 years; however, the definitive molecular mechanism responsible for their therapeutic actions remained uncertain. The conventional pharmacological observation regarding their efficacy in chronic pain modulation is the weakening of glutamate release at presynaptic terminals in the spinal cord. While the α2/δ-1 subunit of voltage-gated calcium channels (VGCCs) has been identified as the primary drug receptor for gabapentinoids, the lack of consistent effect of this drug class on VGCC function is indicative of a minor role in regulating this ion channel's activity. The current review targets the efficacy and mechanism of gabapentinoids in treating chronic pain. The discovery of interaction of α2/δ-1 with thrombospondins established this protein as a major synaptogenic neuronal receptor for thrombospondins. Other findings identified α2/δ-1 as a powerful regulator of N-methyl-D-aspartate receptor (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) by potentiating the synaptic expression, a putative pathophysiological mechanism of neuropathic pain. Further, the interdependent interactions between thrombospondin and α2/δ-1 contribute to chronic pain states, while gabapentinoid ligands efficaciously reverse such pain conditions. Gabapentin normalizes and even blocks NMDAR and AMPAR synaptic targeting and activity elicited by nerve injury. SIGNIFICANCE STATEMENT: Gabapentinoid drugs are used to treat various neurological conditions including chronic pain. In chronic pain states, gene expression of cacnα2/δ-1 and thrombospondins are upregulated and promote aberrant excitatory synaptogenesis. The complex trait of protein associations that involve interdependent interactions between α2/δ-1 and thrombospondins, further, association of N-methyl-D-aspartate receptor and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor with the C-tail of α2/δ-1, constitutes a macromolecular signaling complex that forms the crucial elements for the pharmacological mode of action of gabapentinoids.

The analgesic effects of botulinum neurotoxin by modulating pain-related receptors; A literature review

Botulinum neurotoxins (BoNTs), produced by Clostridium botulinum, have been used for the treatment of various central and peripheral neurological conditions. Recent studies have suggested that BoNTs may also have a beneficial effect on pain conditions. It has been hypothesized that one of the mechanisms underlying BoNTs' analgesic effects is the inhibition of pain-related receptors' transmission to the neuronal cell membrane. BoNT application disrupts the integration of synaptic vesicles with the cellular membrane, which is responsible for transporting various receptors, including pain receptors such as TRP channels, calcium channels, sodium channels, purinergic receptors, neurokinin-1 receptors, and glutamate receptors. BoNT also modulates the opioidergic system and the GABAergic system, both of which are involved in the pain process. Understanding the cellular and molecular mechanisms underlying these effects can provide valuable insights for the development of novel therapeutic approaches for pain management. This review aims to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions by inhibiting the transmission of pain-related receptors.

The Known Biology of Neuropathic Pain and Its Relevance to Pain Management

Patients with neuropathic pain are heterogeneous in pathophysiology, etiology, and clinical presentation. Signs and symptoms are determined by the nature of the injury and factors such as genetics, sex, prior injury, age, culture, and environment. Basic science has provided general information about pain etiology by studying the consequences of peripheral injury in rodent models. This is associated with the release of inflammatory cytokines, chemokines, and growth factors that sensitize sensory nerve endings, alter gene expression, promote post-translational modification of proteins, and alter ion channel function. This leads to spontaneous activity in primary afferent neurons that is crucial for the onset and persistence of pain and the release of secondary mediators such as colony-stimulating factor 1 from primary afferent terminals. These promote the release of tertiary mediators such as brain-derived neurotrophic factor and interleukin-1β from microglia and astrocytes. Tertiary mediators facilitate the transmission of nociceptive information at the spinal, thalamic, and cortical levels. For the most part, these findings have failed to identify new therapeutic approaches. More recent basic science has better mirrored the clinical situation by addressing the pathophysiology associated with specific types of injury, refinement of methodology, and attention to various contributory factors such as sex. Improved quantification of sensory profiles in each patient and their distribution into defined clusters may improve translation between basic science and clinical practice. If such quantification can be traced back to cellular and molecular aspects of pathophysiology, this may lead to personalized medicine approaches that dictate a rational therapeutic approach for each individual.

Long-Term Results of Cortical Motor Stimulation for Neuropathic Peripheral and Central Pain: Real-World Evidence From Two Independent Centers

BACKGROUND AND OBJECTIVES

Cortical motor stimulation (CMS) is used to modulate neuropathic pain. The literature supports its use; however, short follow-up studies might overestimate its real effect. This study brings real-world evidence from two independent centers about CMS methodology and its long-term outcomes.

METHODS

Patients with chronic refractory neuropathic pain were implanted with CMS. The International Classification of Headache Disorders 3rd Edition was used to classify craniofacial pain and the Douleur Neuropathique en 4 Questions Scale score to explore its neuropathic nature. Demographics and clinical and surgical data were collected. Pain intensity at 6, 12, and 24 months and last follow-up was registered. Numeric rating scale reduction of ≥50% was considered a good response. The Clinical Global Impression of Change scale was used to report patient satisfaction.

RESULTS

Twelve males (38.7%) and 19 females (61.3%) with a mean age of 55.8 years (±11.9) were analyzed. Nineteen (61.5%) were diagnosed from painful trigeminal neuropathy (PTN), and seven (22.5%) from central poststroke pain. The mean follow-up was 51 months (±23). At 6 months, 42% (13/31) of the patients were responders, all of them being PTN (13/19; 68.4%). At last follow-up, only 35% (11/31) remained responders (11/19 PTN; 58%). At last follow-up, the global Numeric rating scale reduction was 34% ( P = .0001). The Clinical Global Impression of Change scale punctuated 2.39 (±0.94) after 3 months from the surgery and 2.95 (±1.32) at last follow-up ( P = .0079). Signs of suspicious placebo effect were appreciated in around 40% of the nonresponders.

CONCLUSION

CMS might show long-term efficacy for neuropathic pain syndromes, with the effect on PTN being more robust in the long term. Multicentric clinical trials are needed to confirm the efficacy of this therapy for this and other conditions.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain

BACKGROUNDS

Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain.

METHODS

Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM).

RESULTS

We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration.

CONCLUSIONS

Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

Integration of microbiota and metabolomics reveals the analgesic mechanisms of emodin against neuropathic pain

BACKGROUND AND OBJECTIVE

Neuropathic pain (NeP) induced dysbiosis of intestinal microbiota in chronic constriction injury (CCI) rats. Emodin has analgesic effect but the detailed mechanism is not clear at the present time. This study aims to explore the underling mechanism of action of emodin against NeP with in CCI model.

METHODS

Male SD rats (180-220 g) were randomly divided into three groups: sham group, CCI group, and emodin group. Behavioral tests were performed to evaluate the therapeutic effects of emodin on CCI model. Feces and spinal cords of all rats were collected 15 days after surgery. 16S rDNA sequencing, untargeted metabolomics, qPCR and ELISA were performed.

RESULTS

Mechanical withdrawal thresholds (MWT), thermal withdrawal latency (TWL) and Sciatic functional index (SFI) in emodin group were significantly higher than CCI group (P < 0.05). Emodin not only inhibited the expression of pro-inflammatory cytokines in the spinal cords and colonic tissue, but also increased the expression of tight junction protein in colonic tissue. 16S rDNA sequencing showed that emodin treatment changed the community structure of intestinal microbiota in CCI rats. Untargeted metabolomics analysis showed that 33 differential metabolites were screened out between CCI group and emodin group. After verification, we found that emodin increased the level of S-adenosylmethionine (SAM) and Histamine in the spinal cord of CCI rats.

CONCLUSION

Emodin was effective in relieving neuropathic pain, which is linked to inhibition inflammatory response, increasing the proportion of beneficial bacteria and beneficial metabolites.